Correlation of electrical and optical derivatives in semiconductor lasers using a novel current modulation technique

by 1982- Lakkarsu, Swathi

LAKKARSU, SWATHI. Correlation of electrical and optical derivatives in semiconductor lasers using a novel current modulation technique. (Under the guidance of Prof. Kolbas) The motivation behind this work is to better characterize the Vertical Cavity Surface Emitting Lasers (VCSELs) provided by Honeywell Inc. with derivative measurements based on current modulation. Electrical and optical derivatives (I-V, L-I, dV/dI, d2V/dI2 , dL/dI) have been used to investigate these VCSELs. The new current modulation technique is compared with a prior voltage modulation technique using a standard edge emitting laser diode. The information supplied by I-V, L-I, dV/dI, d2V/dI2, dL/dI have been used to detect laser threshold, quasi Fermi level locking, quantum efficiency, series resistance, current ideality, light ideality and also subtle nonlinearities in the device behavior. Near field images of the optical output have been correlated with the electrical and optical measurements and shown to be consistent with our observation and analysis. Different methods of calculating the laser threshold, series resistance, ideality and quantum efficiency, by plotting appropriate curves, have been identified and were shown to be consistent for the edge emitting laser diode and the two types of VCSELs. This approach has been shown to be good for observing simple devices like the edge emitting laser diode that have a clean structure and also complex devices like the VCSELs, of which the oxide VCSEL was relatively featureless in contrast to the proton VCSEL which exhibited fine structure which we were able to detect and explain. Thus we have been able to show that the derivative measurements provide an accurate and reliable method for determining various parameters in photonic devices by a purely electrical measurement. Combined with optical measurements a powerful tool for understanding the inner workings of VCSELs is demonstrated.